1. Field of the Invention
The invention relates to an injection mold design, a method for in-mold coating of lenses, and the resulting coated lenses.
2. The Prior Art
The methods for coating an injection molded article in situ have been disclosed widely and are commonly referred to as the “in-mold coating” process. Typically, in-mold coating involves injecting coating solution directly into a closed cavity or opening the mold to apply the coating solution on to the just molded parts. Both methods suffer from a common problem, in that coating solution tends to leak out of the mold cavity. This leakage affects the coverage and thickness of the coating on the target part surface. The leaked coating solution may damage the mold as the coating cures along the parting line.
U.S. Published Patent Application 2003/0077425 and U.S. Published Patent Application 2003/0082344 both describe a closed-mold direct coating process, in which a thin coating containment flange is provided around the perimeter of the molded article. The flange prevents the coating from leaking or seeping off the desired surface and out of the mold cavity. The shrinkage of the flange was much smaller than the rest of the part, because the flange is thinner. As a result, the resistance to coating flow was much higher at the flange, which minimized coating leakage.
The Prior Art describes molding one product, like a plaque, where the center-gated mold has been customized for a singular application. In the manufacture of ophthalmic lenses, injection molds are edge-gated and require frequent changes of lens inserts. Accordingly, the solutions of the prior art would not be suitable for providing uniformly thin coatings on a variety of lenses. Hence, it would be desirable to provide a method and apparatus to prevent coating solution from leaking out of a lens molding cavity in order to make an in-mold lens coating process practical.